1. Field of the Invention
The present invention relates to a semiconductor circuit and a semiconductor device, and more particularly to a semiconductor circuit and a semiconductor device both for driving a power semiconductor switching element.
2. Description of the Background Art
Some of level shift circuits included in semiconductor circuits which drive conventional power semiconductor switching elements perform, for example, a function for preventing a malfunction due to self-excited dV/dt (an abrupt change in a floating potential VM generated when a P-side semiconductor switching device is turned off) and another function for preventing a malfunction due to separately excited dV/dt (an abrupt change in a floating potential VM generated by ON/OFF operations of other arms) (see Paragraph [0014] and “Means for Solving the Problems” of Japanese Patent Application Laid Open Gazette No. 9-172366). In this case, dV/dt is an abrupt change in a reference potential generated by ON/OFF operations of a semiconductor switching device described later and can cause a malfunction.
In such a semiconductor circuit, the self-excited dV/dt is expected to be generated within a time period while an ON-side one-shot signal is inputted to a high voltage transistor.
There is a case, however, where no dV/dt is generated until the ON-side one-shot signal is finished because of light load driving of the semiconductor circuit, a delay in response of the P-side semiconductor switching device, a delay in transmission of the level shift circuit, and the like.
At that time, since a circuit structure for decreasing a resistance value of the other system is invalidated and the resistance value of the OFF side is higher than that of the ON side, when dV/dt is applied, an OFF-side pulse is transmitted earlier to a Set-Reset Flip-Flop and this disadvantageously turns off the P-side semiconductor switching device.
In order to avoid the above problem, it is necessary to increase the width of the one-shot signal to be sufficiently longer than the time period from the turn-on of the P-side semiconductor switching device to the application of the dV/dt thereto.
Increasing the width of the one-shot signal, however, arises a problem that a time period while the high voltage transistor is in an ON state becomes longer and the power consumed in the high voltage transistor is increased.
Further, since the time period from the turn-on of the P-side semiconductor switching device to the application of the dV/dt thereto depends on external factors such as the type of P-side semiconductor switching device (current-carrying capacity) and the load average of an inverter circuit or the like, the degree of design freedom for determining the width of the one-shot signal is lower.